U.S. patent application number 13/254854 was filed with the patent office on 2012-01-12 for apparatus and process for atomic or molecular layer deposition onto particles during pneumatic transport.
This patent application is currently assigned to DELFT UNIVERSITY OF TECHNOLOGY. Invention is credited to Jan Rudolf Van Ommen.
Application Number | 20120009343 13/254854 |
Document ID | / |
Family ID | 42167451 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120009343 |
Kind Code |
A1 |
Van Ommen; Jan Rudolf |
January 12, 2012 |
APPARATUS AND PROCESS FOR ATOMIC OR MOLECULAR LAYER DEPOSITION ONTO
PARTICLES DURING PNEUMATIC TRANSPORT
Abstract
The invention provides a process for depositing a coating onto
particles being pneumatically transported in a tube. The process
comprising the steps of providing a tube having an inlet opening
and an outlet opening; feeding a carrier gas entraining particles
into the tube at or near the inlet opening of the tube to create a
particle flow through the tube; and injecting a first
self-terminating reactant into the tube via at least one injection
point downstream from the inlet opening of the tube for reaction
with the particles in the particle flow. The process is suitable
for atomic layer deposition and molecular layer deposition. An
apparatus for carrying out the process is also disclosed.
Inventors: |
Van Ommen; Jan Rudolf;
(Delft, NL) |
Assignee: |
DELFT UNIVERSITY OF
TECHNOLOGY
Delft
NL
|
Family ID: |
42167451 |
Appl. No.: |
13/254854 |
Filed: |
March 4, 2010 |
PCT Filed: |
March 4, 2010 |
PCT NO: |
PCT/EP2010/052769 |
371 Date: |
September 5, 2011 |
Current U.S.
Class: |
427/213 ;
118/716 |
Current CPC
Class: |
C23C 16/45525 20130101;
C23C 16/45551 20130101; C23C 16/4417 20130101; C23C 16/442
20130101; B01J 8/18 20130101 |
Class at
Publication: |
427/213 ;
118/716 |
International
Class: |
C23C 16/442 20060101
C23C016/442; B05D 7/00 20060101 B05D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2009 |
NL |
2002590 |
Claims
1. A process for depositing a coating onto particles being
pneumatically transported in a tube, said process comprising the
steps of: (i) providing a tube having an inlet opening and an
outlet opening; (ii) feeding a carrier gas entraining particles
into the tube at or near the inlet opening of the tube to create a
particle flow through the tube; and (iii) injecting a first
self-terminating reactant into the tube via at least one injection
point downstream from the inlet opening of the tube for reaction
with the particles in the particle flow.
2. The process of claim 1, wherein the particles comprise
agglomerates of smaller particles.
3. The process of claim 1 or claim 2, wherein the first reactant is
injected into the tube via a plurality of injection points
downstream from the inlet opening of the tube, and an injection
point downstream from another injection point is arranged to
increase the velocity of the carrier gas.
4. The process of claim 3 wherein the injection points are spaced
along at least a portion of the length of the tube.
5. The process of claim 4 wherein the injection points are spaced
along substantially the length of the tube.
6. The process of any one of the preceding claims, further
comprising pre-conditioning the particles in the tube upstream of
an injection point.
7. The process of any one of the preceding claims, further
comprising injecting a second self-terminating reactant into the
tube via at least one further injection point downstream from the
at least one injection point for reaction with particles in the
particle flow.
8. The process of claim 7, wherein the first reactant is a
precursor for the second reactant.
9. The process of claim 7 or 8, wherein the further injection point
is arranged to increase the velocity of the carrier gas.
10. The process of any one of the preceding claims, wherein the
carrier gas is fed at such velocity that the carrier gas velocity
is greater than the particle velocity in the particle flow.
11. The process of any one of the preceding claims, wherein the
particle flow takes the form of a plug flow.
12. The process of any one of the preceding claims further
comprising removing reaction by-products from the tube at least one
flush point.
13. The process of claim 12 wherein reaction by-products are
removed from the tube at a plurality of flush points spaced along
the length of the tube.
14. The process of any one of the preceding claims, further
comprising keeping different parts of the tube at different
temperatures.
15. The process of any one of the preceding claims, wherein the
tube is provided with a plurality of injection points numbered
sequentially from the inlet opening of the tube; wherein a first
self-terminating reactant is injected into the odd-numbered
injection points; and a second self-terminating reactant is
injected into the even-numbered injection points.
16. The process of claim 15, wherein the injection points are
spaced such that a self-terminating reaction is substantially
self-terminated between injection points.
17. The process of claim 15 or claim 16, further comprising:
keeping tube segments downstream from odd-numbered injection points
and upstream to even-numbered injection points at a first
temperature; and keeping tube segments downstream from
even-numbered injection points and upstream to odd-numbered
injection points at a second temperature.
18. The process of any one of the preceding claims wherein the
carrier gas is an inert gas.
19. The process of any one of the preceding claims wherein the
carrier gas travels through the tube at a linear velocity of from
0.02 to 30 m/s, preferably from 0.1 to 10 m/s.
20. The process of any one of the preceding claims wherein the
particle size of the particles being coated is in the range of from
2 nm to 1 mm.
21. Apparatus comprising: (i) a tube having an inlet opening and an
outlet opening; (ii) a feeder device for feeding a carrier gas
entraining the particles into the tube; and (iii) at least one
injection point downstream from the inlet opening for introducing a
reactant into the tube; wherein the apparatus is arranged to
perform the process of any one of claims 1-20.
22. The apparatus of claim 21, wherein the apparatus comprises a
plurality of injection points spaced apart along at least a portion
of the length of the tube.
23. The apparatus of claim 21 or claim 22, wherein the tube is
provided with a plurality of injection points numbered sequentially
from the inlet opening of the tube; wherein odd-numbered injection
points are arranged for injection of a first self-terminating
reactant; and even-numbered injection points are arranged for
injection of a second self-terminating reactant.
24. The apparatus of any one of claims 21-23, further comprising at
least one flush point for removing reaction by-products from the
tube.
25. The apparatus of claim 24 comprising a plurality of flush
points along at least part of the length of the tube.
26. The apparatus of any one of claims 21-25, wherein the tube has
an internal diameter in the range of from 0.02 mm to 300 mm,
preferably in the range of from 1 mm to 20 mm.
27. The apparatus of claim 26, wherein the tube has an internal
diameter in the range of from 1 mm to 20 mm.
28. The apparatus of any one of claims 21-27, wherein the tube has
a length of from 0.1 m to 500 m.
29. The apparatus of claim 28 wherein the tube has a length of from
5 to 50 m,
30. The apparatus of any one of claims 21-29, wherein the tube is
folded or coiled.
31. The apparatus of any one of claims 21-30, wherein the tube is
contained in a chamber provided with means for heating and/or means
for cooling.
32. The apparatus of claim 31 wherein the chamber can be kept at a
temperature in the range of from 0.degree. C. to 1000.degree.
C.
33. The apparatus of claim 31, wherein different parts of the tube
can be kept at different temperatures.
34. The apparatus of claim 23, wherein tube segments downstream
from odd-numbered injection points and upstream to even-numbered
injection points are arranged to be kept at a first temperature,
and tube segments downstream from even-numbered injection points
and upstream to odd-numbered injection points are arranged to be
kept at a second temperature.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to a continuous process for
depositing layers onto small particles, and more particularly to a
continuous process for atomic or molecular layer deposition onto
small particles, in particular nanoparticles.
[0003] 2. Description of the Related Art
[0004] Several techniques are known for depositing layers of a
material onto a solid substrate. Examples include electroplating;
electroless plating; chemical vapor deposition; and atomic or
molecular layer deposition. The various techniques are essentially
carried out in batch mode, and the deposition process may have to
be repeated several times in order to obtain a coating of a
specific desired thickness. As a result, the state of the art
processes tend to be cumbersome and expensive.
[0005] GB 2 214 195 A discloses a pneumatic transport reactor for
coating particles with a metal, for example Ni, Fe or Co, by
decomposing the gaseous carbonyl of the metal thermally on the
heated surface of the particles. The apparatus is constructed in
the form of a loop, comprising a downwardly extending section and
an upwardly extending section. The particles are mixed with a
carrier gas containing the metal carbonyl in the downward section.
The carbonyl is decomposed in the upward section, depositing metal
on the particle. The apparatus comprises a separator, such as a
cyclone, for separating the particles from the carrier gas.
[0006] The apparatus is suitable for particles having a particle
size in the lower micron range, on the order of 4 .mu.m. The
particles may be circulated through the closed loop until the
desired coating thickness is achieved, in what is essentially a
batch-wise operation.
[0007] Puurunen, "Surface chemistry of atomic layer deposition: A
case study for the trimethylaluminum/water process" Journal of
Applied Physics 97, 121301 (2005) provides an overview of atomic
layer deposition techniques in general, and of alumina in
particular. In essence, atomic layer deposition ("ALD") is a
specific form of chemical vapor deposition, based on
self-terminating gas-solid reactions.
[0008] The growth of layers by ALD consists of repeating reaction
cycles consisting of four steps:
(1) A self-terminating reaction of a first reactant (Reactant A)
with the surface of a solid substrate; (2) A purge or evacuation to
remove non-reacted Reactant A and any gaseous reaction by-products;
(3) A self-terminating reaction of a second reactant (Reactant B),
or another treatment to activate the surface of the substrate again
for a reaction with Reactant A. (4) A purge or evacuation of excess
Reactant B and of gaseous reaction products produced in step
(3).
[0009] Step (1) is self-terminating in the sense that it stops when
a monolayer is formed. A monolayer, in the context of ALD, is
formed when all chemisorption sites available for Reactant A at the
surface of the substrate are occupied. An important advantage of
ALD is that layers are deposited epitaxially, resulting in a
coating that is well defined down to an atomic scale. However, with
ALD, by definition, only one atomic layer is deposited in each
reaction cycle. For the formation of a relatively thick coating ALD
may thus be less suitable, as the deposition of such coating may
require tens, sometimes hundreds or even thousands of reaction
cycles.
[0010] US Published Patent Application 2006/0062902 A1 discloses
use of ALD for producing CIGS particles for use in photovoltaic
panels. The particles are agitated to form a fluidized bed during
coating, so that all the surface area of the suspended particle is
accessible for surface reactions.
[0011] Helmsing et al., "Short Contact Time Experiments in a Novel
Benchscale FCC Riser Reactor", Chemical Engineering Science, Vol.
51, No. 11, pp 3039-3044 (1996) disclose an entrained flow reactor
consisting essentially of a long, thin tube. The tube is looped so
as to fit in a heating chamber of a manageable size. The reactor
can be operated under plug flow conditions, making it suitable for
testing catalysts used in fluid catalytic cracking ("FCC") of crude
oil fractions. The reactor has a single injection point for
reactants.
[0012] Thus, there is a particular need for a continuous process
for depositing atomic or molecular layers onto small particles, and
for an apparatus for carrying out such a continuous process.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention addresses these problems by providing
a process for depositing sequential layers onto particles being
pneumatically transported in a tube, the process comprising the
steps of (i) providing a tube having an inlet opening and an outlet
opening; (ii) feeding a carrier gas entraining particles into the
tube at or near the inlet opening of the tube to create a particle
flow through the tube; injecting a first self-terminating reactant
into the tube via at least one injection point downstream from the
inlet opening of the tube for reaction with the particles in the
particle flow. The injection of reactant into a particle flow in a
tube for reaction with these particles enable a continuous process
of layer deposition on particles.
[0014] Another aspect of the invention comprises an apparatus for
depositing sequential layers onto particles while the particles are
subjected to pneumatic transport, the apparatus comprising (i) a
tube having an inlet opening and an outlet opening; (ii) a feeder
device for feeding a carrier gas entraining the particles into the
tube; and (iii) at least one injection point downstream from the
inlet opening for introducing a reactant into the tube, wherein the
apparatus is arranged to perform abovementioned process.
BRIEF DESCRIPTION OF THE DRAWING
[0015] The features and advantages of the invention will be
appreciated upon reference to the following drawing, in which:
[0016] FIG. 1 is a schematic view of an embodiment of the apparatus
of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The invention relates to a continuous process or method for
depositing sequential layers onto particles being pneumatically
transported in a tube, said process comprising the steps of (i)
providing a tube having an inlet opening and an outlet opening;
(ii) feeding a carrier gas entraining particles into the tube at or
near the inlet opening of the tube; injecting a reactant into the
tube via at least one injection point downstream from the inlet
opening of the tube.
[0018] The process is suitable for depositing layers by an atomic
layer deposition process and/or a molecular layer deposition
process. The particles may include agglomerates formed by smaller
particles. Such agglomerates allow for pneumatic transport of very
small particles, while the surface of these very small particles
remain available for reaction with the reactant. Throughout the
description, the term "particles" may refer to both particles and
agglomerates formed by these particles.
[0019] In a preferred embodiment of the process, the particles
travel through the tube in substantially a plug flow. Although the
term "plug flow" may suggest that the particles travel at the same
linear velocity as the carrier gas, for larger particles this is
not the case. With particles larger than several micrometers there
is a certain amount of slippage between the carrier gas and the
entrained particles, such that the carrier gas travels at a greater
velocity than do the particles. Under those circumstances, due to
this slippage, the reactor is essentially self-purging: unreacted
reactants and reaction products are removed from the particles by
carrier gas overtaking and passing the particles.
[0020] This self-purging aspect of the process of the invention
contributes to the ability of the process to be operated in a
continuous mode, which makes the process attractive for conducting
atomic or molecular layer deposition reaction cycles. As, in
general, it is desirable to deposit more than one layer onto the
particles, a preferred embodiment of the process uses a plurality
of injection points downstream of the inlet opening of the
tube.
[0021] This self-purging effect is not present when the particle
size is too small for any significant slippage to take place. The
process of the invention can be used even under these circumstances
for depositing a small number of layers. For example, when
preparing catalyst particles it is oftentimes sufficient to deposit
only one layer.
[0022] Even for depositing a larger number of layers onto small
particles the process of the invention is useful. For this
embodiment of the process it may be desirable to provide the tube
with purge ports for removing reaction by-products and unreacted
reactants.
[0023] In traditional chemical vapor deposition each reactant
injection point corresponds to the deposition of a layer onto the
particle. This layer is not necessarily a monolayer. For example,
the process may be used for depositing a metal, such as Ni, Fe, or
Co, whereby a corresponding organometallic compound is injected
into the first reactant injection point. The tube may be kept at a
temperature sufficiently high to cause decomposition of the
organometallic compound. In general, temperatures in the range of
100 to 320.degree. C. are suitable, the lower limit being governed
by the decomposition temperature of the organometallic compound.
Alternatively, a plasma could be used to activate the reaction.
[0024] Upon entering the tube the organometallic compound
decomposes, and the metal is deposited onto the particles entrained
by the carrier gas. The organic compound produced in the
decomposition reaction of the organometallic compound is removed
from the particles by the carrier gas. The deposition cycle is
repeated upon injection of organometallic compound at the second
injection point, whereby a second layer of metal is deposited onto
the particle. In general, when the process is used in traditional
chemical vapor deposition, the number of layers deposited onto the
particles is identical the number of injection points receiving
organometallic compound.
[0025] The term "traditional chemical vapor deposition" as used
herein generally refers to single-reactant chemical vapor
deposition or multiple reactants added at the same time, in which
the reaction is not self-terminating. Atomic Layer Deposition
("ALD") can be considered a specific embodiment of chemical vapor
deposition. In ALD, only one atomic layer is deposited in each
reaction cycle. In particular, the term "Atomic Layer Deposition"
or "ALD", as used herein, refers to a chemical vapor deposition
process in which a reactant is deposited onto the surface of the
particles in a self-terminating reaction. In many cases the process
cycle comprises a second reaction step, in which a second reactant
is contacted with the particle surface. The term ALD as used herein
is, however, not limited to this dual reactant process, as other
means may be used to activate the surface of the particle for a
subsequent reaction with the first reactant.
[0026] Importantly, depending on the specific reactants, the
"atomic" layer being deposited may in fact be a molecular layer.
The term ALD as used herein encompasses also molecular layer
deposition.
[0027] The ALD process will be explained with reference to a dual
reactant ALD reaction cycle. The first reactant is injected into
the first injection point. This first reactant is a precursor of
the atom or molecule to be deposited onto the surface of the
particles. The first reactant interacts with the particles to form
a chemisorption monolayer onto the surface of the particles. If
gas/particle slippage occurs, unreacted first reactant and reaction
by-products are removed from the particles by the self-purging
mechanism described above.
[0028] The second reactant is injected into the second injection
point. Upon entering the tube, the second reactant comes into
contact with the particles, which are covered with a monolayer of
(a reaction product of) the first reactant. The second reactant
reacts with the chemisorbed (reaction product of) the first
reactant to form the atom or molecule layer of the desired coating
material. If gas/particle slippage occurs, unreacted second
reactant and reaction by-products are removed from the particles by
the self-purging mechanism.
[0029] A second ALD layer may be deposited by injecting the first
reactant into a third injection point, and the second reactant into
a fourth reaction point, and so on. In general, a large number of
layers can be deposited by providing a large number of injection
points along the tube. The first reactant is injected into
injection points 1, 3, 5, etc. (counting from the inlet opening and
going downstream); the second reactant is injected into injection
points 2, 4, 6, etc. In general, the first reactant is injected
into the odd-numbered injection points, and the second reactant is
injected into the even-numbered injection points.
[0030] The self-purging mechanism described above is an idealized
model, which is generally met only in tubes having a single
injection point. Particles located at a second injection point are
purged by a carrier gas comprising small quantities of unreacted
reactant and/or reaction by-products from the first reaction point.
In general these contaminants are sufficiently diluted not to cause
problems. In particular if the tube contains a large number of
injection points, it may be desirable to provide one or more flush
points for removing reaction products and/or unreacted
reactants.
[0031] Desirably, the carrier gas is an inert gas, for example
nitrogen or a noble gas, in particular helium.
[0032] The linear velocity of the carrier gas is selected to be
high enough to cause entertainment of the particles. Accordingly,
the lower limit of this linear velocity is largely determined by
factors such as the mean particle size, the particle density, and
the aspect ratio of the particles. It will be understood that the
particle size increases as the particles travel through the tube,
as a result of the coating layers being deposited onto the
particles. The linear velocity of the carrier gas should be
sufficient for entraining the particles after deposition of the
desired number of coating layers. For this purpose, the linear
velocity may be increased along the tube. In some embodiments such
velocity increase is at least partially obtained by the subsequent
reactant injections.
[0033] In an alternate embodiment of the process the tube is
provided with one or more flush points, which are used not only to
flush the carrier gas, but also to increase the carrier gas flow
rate by introducing more carrier gas than is being flushed out. As
a result the linear velocity of the carrier gas is increased
downstream from the flush point, to compensate for the increase in
weight and size of the particles.
[0034] The upper limit of the linear velocity of the carrier gas is
determined primarily be the desire to operate the tube under plug
flow conditions. The principles of plug flow are well known to
those skilled in the art. The conditions for plug flow for a tube
similar to the one used in the process of the invention are
disclosed in Helmsing et al., "Short Contact Time Experiments in a
Novel Benchscale FCC Riser Reactor", Chemical Engineering Science,
Vol. 51, No. 11, pp 3039-3044 (1996), the disclosures of which are
incorporated herein by reference.
[0035] The linear velocity is preferably chosen so as to obtain
completion of the self-terminating reaction before the next
injection point is encountered. In general, the linear velocity of
the carrier gas is in the range of from 0.02 to 30 m/s, preferably
in the range of from 0.1 to 10 m/s.
[0036] The tube is kept at a temperature suitable for the reaction
cycles being carried out within the tube. In general, the
temperature is in the range of from 0 to 1000.degree. C. In ALD the
first and second reactions of a reaction cycle may require
different reaction temperatures. In a preferred embodiment of the
invention different parts of the tube may be kept at different
temperatures. Specifically, tube segments downstream from
odd-numbered injection points and upstream to even-numbered
injection points are kept at a first temperature, corresponding to
the reaction temperature of the first reaction of the ALD reaction
cycle. Likewise, tube segments from even numbered injection points
to odd numbered injection points are kept at a second temperature,
corresponding to the reaction temperature of the second reaction of
the ALD reaction cycle.
[0037] Optionally, before reaching an injection point, particles in
the tube may be pre-conditioned. Particle pre-conditioning can be
particularly useful before particles are brought into contact with
the first reactant, i.e. upstream the first injection point.
Pre-conditioning may include heating of the particles upstream an
injection point to a desired temperature, preferably a temperature
corresponding or close to the reaction temperature of the reaction
planned downstream the injection point. Pre-heating of particles
upstream the injection point may limit development of a temperature
gradient in the tube downstream of the injection point. The
presence of such temperature gradient is undesirable as it may
induce different reaction rates in different portions of the tube.
A substantially constant temperature at different portions of the
tube provides a more constant reaction rate, which simplifies
reaction control and apparatus design.
[0038] Additionally, or alternatively, reactants injected in the
tube may also be pre-heated to a suitable temperature before they
are injected into the tube for similar reasons as discussed above
with respect to the pre-heating of the particles.
[0039] Tube segments from even-numbered injection points to
odd-numbered injection points may be made of a different material
than tube segments from odd-numbered injection points to
even-numbered injection points to accommodate reactions at
different temperatures and/or cope with different reactants and/or
gaseous reactant products. For example, some tube segments may be
made of Teflon, while others may be made of stainless steel. The
selection of a suitable tube material may be based on finding an
optimum in chemical resistance and heat conduction properties. For
example, if keeping a constant temperature throughout the tube is
of importance, a tube material with a sufficiently high heat
conduction coefficient is desirable. Additionally, it may be
desirable that the reaction between particles and injected
reactants is not disturbed by chemical reactions with binding
groups in the tube walls. Therefore, if such reactions are likely
to occur due to the use of a specific type of reactants, a material
with sufficient resistance against such chemical reactions is
desirable.
[0040] The process is suitable for depositing coatings onto
particles of a broad range of mean particle sizes, from about 2 nm
to 1 mm. An important advantage of the process of the invention, as
compared to fluidized bed processes of the prior art, is its
ability to coat particles having a particle size well below 1
mm.
[0041] Another aspect of the present invention is an apparatus for
carrying out the above-described process. In its broadest aspect
this aspect relates to an apparatus for a continuous process for
atomic layer deposition onto particles while said particles are
subjected to pneumatic transport, said apparatus comprising (i) a
tube having an inlet opening and an outlet opening; (ii) a feeder
device for feeding a carrier gas entraining the particles into the
tube; and (iii) at least one injection point downstream from the
inlet opening for introducing a reactant into the tube.
[0042] In a preferred embodiment the tube has a plurality of
injection points downstream from the inlet opening. Desirably the
injection points are spaced apart along at least a portion of the
length of the tube. Preferably the injection points are spaced
along substantially the length of the tube.
[0043] A preferred embodiment of the apparatus comprises at least
one flush point for removing reaction by-products from the tube.
The term "reaction by-products" in this context includes unreacted
reactants.
[0044] The tube has an internal diameter in the range of from 0.02
to 300 mm. The actual diameter may be selected within this range in
function of the mean diameter of the particles to be coated within
the apparatus, the desired linear velocity of the carrier gas, and
like such factors. In most cases a suitable tube inner diameter is
in the range of from 0.1 mm to 100 mm, preferably in the range of
from 1 mm to 20 mm.
[0045] If there is more than 1 injection point, the distance
between to adjoining injection points is preferably determined by
the time required for the reaction to self-terminate, and the
distance traveled by the carrier gas during that time. The
reactions involved are generally more or less instantaneous, but
some time needs to be allowed for the reactants to travel from the
injection point to the particles. In general, subsequent injection
points are from 10 mm to 5000 mm apart, preferably from 10 mm to
100 mm apart.
[0046] The length of the tube is determined primarily by the number
of injection points required. Accordingly, the length of the tube
is in the range of from 0.1 m to 500 m. In many cases the length of
the tube is in the range of from 5 m to 50 m.
[0047] In order to limit the physical space requirements of the
apparatus the tube may be folded or coiled. Suitably, the tube is
contained in a chamber provided with means for heating and/or
cooling. The actual design of the chamber, and the specifications
of the heating and/or cooling means, may be based on the desired
operating temperature. The operating temperature may be in the
range of from 0.degree. C. to 1000.degree. C.
[0048] FIG. 1 is a schematic representation of an embodiment of the
apparatus of the invention for deposing a number of layers onto
particles entrained in a flow of gas. Particles 10 are fed into
fluidizer 100 where they are fluidized by inert gas 11, e.g.
nitrogen, and entrained into a coiled tube 1. At first injection
point 12A the first reactant of an atomic layer deposition cycle is
introduced into the coiled tube. At second injection point 12B the
second reactant of the ALD cycle is introduced into the coiled
tube. At injection point 13A a second dose of the first reactant is
introduced, and at injection point 13B the coiled tube receives a
second dose of the second reactant. The cycle is repeated at
injection point pairs 14A/14B; 15A/15B; and 16A/16B. A separation
device 200 separates the coated particles 18 from the gas flow 17,
which may now not only comprise the inert gas, but also gaseous
reaction products, and unreacted reactants. The separation device
200 may be any suitable separation device, for example a cyclone
separator.
[0049] Optionally, as denoted by the dashed arrows, one or more
flush points 12-16C, 12-16D are arranged along the tube to remove
gaseous reaction products from the gas flow. In particular, flush
points 12C, 13C, 14C, 15C and 16C may predominantly remove gaseous
reaction products related to the first reactant. Similarly, flush
points 12D, 13D, 14D, 15D, and 16D may predominantly remove gaseous
reaction products related to the second reactant. The flush points
may comprise a suitable filter to allow reaction products to be
removed while keeping particles in the tube 1.
[0050] Optionally, the temperature of the different reactions may
be set by temperature control units 21, 22, for example heat
exchangers or other types of devices for heating and/or cooling
known to a person skilled in the art. The temperature control units
21 may be arranged to control the temperature in parts of the tube
reserved for reaction with the first reactant, i.e. downstream
injection points of the first reactant and upstream injection
points of the second reactant. For example, the temperature control
units 21 may be arranged to keep the temperature in these tube
parts at a first temperature. Similarly, the temperature control
units 22 may be arranged to control the temperature in tube parts
reserved for reaction with the second reactant, e.g. by keeping the
temperature in these parts at a second temperature.
[0051] Optionally, a pre-conditioning unit 23 is arranged for
pre-conditioning the particles in the particle flow. Such
pre-conditioning may include heating particles to a temperature
close to a desirable reaction temperature with the first reactant
provided via injection point 12A. Although not explicitly shown,
more pre-conditioning units may be used in the apparatus, for
example to pre-heat particles upstream further injection
points.
It will be understood that the representation is a schematic one.
The depicted number of injection point pairs (numbering 5 in FIG.
1) represents a plurality of injection point pairs which, in
reality, may range from just 1 to several hundreds or even
thousands.
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